High-level staff changes continued at the Smithsonian yesterday with the resignation of Robert Dierker from his position as deputy assistant secretary for media affairs. Dierker will become special media adviser to Roger Kennedy, head of the Museum of American History.

Dierker didn't respond to inquiries about his departure from his high-level staff position.

Known for an aggressive, hard-driving style, Dierker worked on "Invention," a cable series hosted by Kennedy. He was also working on a series on the quincentenary of Columbus's voyage to America from a Latin American perspective. Dierker reported to Tom Lovejoy, assistant secretary for external affairs.

Spokeswoman Madeleine Jacobs confirmed that Dierker has resigned. "We feel that Bob has done an excellent job. We are delighted that Roger Kennedy will have his services," she said.

Last month, the Smithsonian restructured several senior staff positions, accepted the resignation of Tom McCance, the director of membership and development, and made John Jameson, assistant secretary for administration since 1976, a senior adviser. Treasurer Ann Leven previously left to become deputy treasurer at the National Gallery of Art.

In July, Undersecretary Dean Anderson was abruptly fired. At that time, Dierker was outspoken in Anderson's support. Carmen Turner, general manager of Metro, will replace Anderson Dec. 16. Sources at the Smithsonian said they expect more changes in coming weeks.

Dierker started at the Smithsonian in 1975 as assistant general counsel. He became associate general counsel in 1985 and was named to a newly created media affairs position in 1988. His responsibilities included day-to-day operation of the office of telecommunications and oversight of the Smithsonian magazine and other publications. In September, Dierker represented the Smithsonian in accepting an Emmy for outstanding informational series for "Smithsonian World," a co-production with WETA-TV.